Stabilizer (ship)

This article is about the nautical term. For other uses, see Stabilizer.

Location and diagram of retractable fin stabilizers on a ship.

Photograph of ship stabilizers: a fixed fin stabilizer (front) and bilge keels.

Ship stabilizers are fins mounted beneath the waterline and emerging laterally. In contemporary vessels, they may be gyroscopically controlled active fins, which have the capacity to change their angle of attack to counteract roll caused by wind or waves acting on the ship.

The bilge keel is an early 20th century predecessor. Although not as effective at reducing roll, bilge keels are cheaper, easier to install, and do not require dedicated internal space inside the hull.

In November 1932 the ship Conte di Savoia made its maiden voyage. It had three huge gyroscopes fitted low down in a forward hold. These rotated at high revolutions and were designed to eliminate rolling - a persistent problem on the rough North Atlantic crossing that affected all shipping lines. Each of the three flywheels was 13 feet in diameter and weighed 108 tons.

The first mention of automatic stabilizers for ships was in 1932, by an engineer working for General Electric.

The first use of fin stablizers on a ship was by a Japanese cruise liner in 1933.

In 1934 a Dutch liner introduced one of the world's most unusual ship stabilizer systems, in which two large tubes were mounted on each side of the ship's hull with the bottom of the tubes open to the sea. The top of the tubes had compressed air or steam pumped in. As the ship rolled the side it was rolling to would fill with water and then compressed air or steam would be injected to push the water down countering the roll.

In 1954 Standford University, developed another system similar to the 1934 Dutch system where a U-shaped water tank is built into a ships hull and as the ship rolls in one direct, water pumps move the water in the U-shape water tank to the other direct. It never was accepted by the marine community.